A Peripheral Component Interconnect (PCI) device is a piece of computer hardware that plugs directly into a PCI slot on a computer's motherboard. Examples of PCI devices include, but are not limited to: network interface cards, audio cards, and sound cards. Each Base Address Register (BAR) of a PCI device attached to a PCI bus requires a pre-defined amount of system memory address space. The particular system requirements such as size, alignment, and starting address of each BAR determine how the memory address space is allocated.